Pump for zinc-rich materials or the like

ABSTRACT

A pump for use in the airless spraying of zinc-rich materials or the like is disclosed. The pump is provided with valves in which the mating valve surfaces are constructed to avoid excessive localized pressure and incorporate elements formed of materials with which zinc-rich coating materials or the like do not tend to form weld type bonds. In one embodiment, a ball check valve includes a rigid ball encased in a polyurethane jacket which seats against a spherical valve seat. In another embodiment, the valve seat is provided by an O-ring formed of elastomeric material.

Waited States Patent [191 Dane et a1.

[ Jan. 22, 1974 1 1 PUMP FOR ZINC-RICH MATERIALS on THE LIKE [75]Inventors: Oscar Dane, Houston; Ronald Wentworth Beers, Spring; GustaveStanley Levey, Houston, all of Tex.

[73] Assignee: Gustave S. Levey, trustee, Houston,

Tex.

[22] Filed: Mar. 24, 1971 [211 App]. No.1 127,676

52 us. (:1 417/554, 417/566, 137/533.11 s1 rm. CI. F04b 21/06 [58] Fieldof Search 417/554, 900, 566; 137/533.11

[56] References Cited UNITED STATES PATENTS 1,991,342 2/1935 BaIl417/552 3,052,259 4/1962 Van Der Volden 251/368 3,059,667 10/1962Coceano 251/368 3,091,254 5/1963 Kilayko 251/368 3,176,713 4/1965McDei-mott 251/368 3,395,890 8/1968 Eckert et a1. 251/368 1,380,4156/1921 Putnam 137/533.11 2,747,510 5/1956 Seggern 417/566 2,895,4217/1959 Peeps 417/554 2,862,478 12/1958 Staats 417/403 3,168,045 2/1965baStigIIl.. 417/900 3,363,580 1/1968 Loguem 417/554 FOREIGN PATENTS ORAPPLICATIONS 333,628 9/1903 France l37/533.ll

Primary Examiner-William L. Freeh Attorney, Agent, or FirmMcNenny,Farrington, Pearne & Gordon [5 7] ABSTRACT A pump for use in the airlessspraying of zinc-rich materials or the like is disclosed. The pump isprovided with valves in which the mating valve surfaces are constructedto avoid excessive localized pressure and incorporate elements formed ofmaterials with which zinc-rich coating materials or the like do not tendto form weld type bonds. In one embodiment, a ball check valve includesa rigid ball encased in a polyurethane jacket which seats against aspherical valve seat. In another embodiment, the valve seat is providedby an O-ring formed of elastomeric material.

14 Claims, 5 Drawing Figures 1 PUMP FOR ZINC-RICH MATERIALS OR THE LIKEBACKGROUND OF THE INVENTION This invention relates generally to pumpingsystems and more particularly to a novel and improved pump suited foruse in airless spray coating systems with zincrich coating materials orthe like.

Zinc-rich coating products have as a principal component powdered zincwith a content from about 25 percent to as much as 70 percent solids byvolume or from about 25 percent to 95 percent solids by weight. Thesematerials are usually divided into two main families consisting of theethyl silicate vehicle type and the alkali metal silicate vehicle type.The zinc-rich coatings with the ethyl silicate vehicle are usually inthe lower solids content category of 30 percent to 40 percent solids byvolume and use organic solvents such as xylene, glycol ethers oralcohols. The second family of zincrich coatings with the alkali metalsilicate vehicle is usually compounded with a 45 percent to 60 percentsolids by volume and water is the solvent base. A third family includesthe quatermary ammonium silicate with weight and volume characteristicssimilar to alkali metal coating. Such zinc-rich coatings are usuallyapplied over a properly prepared metal surface, normally sandblasted toproduce a particular anchor pattern, and provide a high level ofcorrosion resistance. Such coatings are often required, for example, onstructures used in the marine, petrochemical, and utilities fields.

Such coatings have in the past normally been applied with a conventionalpaint spray pressure pot and a conventional air atomizing spray gun.Such application is subject to many disadvantages. For example, theethyl silicate vehicle coatings are moisture cured in that theypolymerize by exposure to moisture. Consequently, they tend to besubject to premature polymerization as a result of moisturecontamination from the air supply used in the conventional pressure pot,hose and air gun. Further, because of the heavy solids characteristic ofsuch zinc-rich coatings, it has been impractical to drive the coatingmaterial from the conventional pressure pot to any working position inexcess of or feet above the level of the supply pot. In addition, sincethere is a tendency for the heavy materials to settle and separate, thelength of the hose has had to be restricted. Still further, conventionalair spraying of the zinc-rich coating causes objectionable overspraywhich tends to cause damage to downwind objects and represents asubstantial material loss as overspray waste. Further, air sprayingmakes application of a wet film in hot, windy weather almost impossiblewith a consequent tendency to mud cracking in the dry film. A powderynon-cohesive film may result. Also, it imposes limitation on thethickness of the coating that may be applied and subjects the work tothe risk of atmospheric contamination after a first conventional airspray coating is applied and before the second coating can be appliedover the first coat.

It has been recognized that these and other problems could be eliminatedor minimized if airless spraying could be used for the spray coating ofsuch zinc-rich coatings or the like. For example, an airless pumpoperating in the range of 600 psi to 1,500 psi has ample power to liftthe material any required distance and is not subject to the height ordistance limitations of the air spray systems described above. Withairless spray- PRIOR ART The recognized advantages of airless sprayinghave in the past been available only in the spray application ofzinc-rich materials in which the solids constitute between 20 percentand 40 percent solids by volume, usually in an organic solvent system.In the past, it has been completely impractical to attempt to useairless spray equipment for the zinc-rich materials having the highersolid content because the reciprocating pumps of such systems havemalfunctioned and lost the ability to pump within five to 15 minutesafter operation has been commenced. The length of the operation period,without malfunction, was usually an inverse proportion of the solidcontent of the material being sprayed.

A pump of the type generally utilized to pressurize and pump the paintin an airless spray system is illustrated in United States Letters Pat.Nos. 3,018,968 and 3,336,066. In such pumps, a piston is reciprocated ina cylinder by an air actuator. A check valve is provided in the lowerend of the cylinder and operates to permit flow only in a directiontoward the main pumping chamber. A second check valve carried by thepiston permits flow only from the main pumping chamber toward thesecondary pumping chamber and therefrom into the discharge line.

In the past, it has been believed that the malfunctioning of such pumpswhen pumping zinc-rich coating materials or the like resulted frompacking of the pump which caused the check valves to malfunction. Theconventional pumps, of the type illustrated in the Letters Patent,supra, normally employ check valves consisting of a hardened steel ballwhich seals against a conical valve seat formed in a tungsten carbideseat member.

SUMMARY OF THE INVENTION In accordance with the present invention, anovel and improved pump structure employs ball check valves which havebeen found in actual practice to function satisfactorily over extendedperiods of time, even when pumping zinc-rich coating materials having asolid content as high as percent by weight. Such pumps functionsatisfactorily and provide at least the same order of service life andreliability as has been encountered in similar prior art pumps when suchpumps were employed to pump typical paint materials.

We have discovered that the conventional prior art pumps have failed notfrom packing," but rather from the formation of a weld type deposit ofthe zinc material on the valve elements.

In the preferred embodiment of this invention, the deposit problem isavoided by substantially reducing the unit pressure occurring betweenthe ball valve and the seat and by utilizing materials with which themetal powder in the coating material does not form a weld type bond. Inone illustrated embodiment, the valve seat member is formed of metalsuch as carbon steel or a stainless steel shaped to provide a seat whichconforms to the shape of the ball check valve element. In suchillustrated embodiment, the ball element is formed with a rigid,preferably brass, ball core encased within a jacket of an elastomericmaterial such as polyurethane or the like. The polyurethane, because itis elastic, deforms a sufficient amount to permit full seating of theball along the entire area of the spherical mating seat. This greatlyreduces the pressure of such engagement thereby greatly reducing thetendency of the zinc to pressure weld in the valve. Further, thepolyurethane material has the physical character of not providing a weldtype bond with zinc. This further inhibits the build-up of zinc depositson the valve elements. The

increased surface area of the valve seat also prevents excessive wear ofthe elastomeric surface of the ball valve as compared to a conventionalvalve seat.

In another illustrated embodiment, the valve seat surface is provided byan elastomeric material and is used either with a ball element of thetype used in the first embodiment or with a simple steel ball. Here,again, the elastomeric material deforms when the valve closes to preventthe occurrence of excessively high pressures along the area ofengagement and also provides a surface on which the zinc does notdeposit with a weld type bond.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofan airless spray system provided with a pump in accordance with thepresent invention;

FIG. 2 is an enlarged fragmentary section of the pump illustrating thestructural arrangement thereof;

FIG. 3 is an enlarged fragmentary section of the ball check valvemounted at the lower end of the cylinder wherein the seat is sphericaland the ball valve element consists of a rigid steel ball core encasedwithin an elastomeric jacket such as polyurethane;

FIG. 4 is an enlarged fragmentary view of a ball check valve, in itsopen position, in accordance with a second embodiment of this inventionin which the valve seat is provided with an elastomeric O-ring typesealing element, and the ball valve element has the same structure asthe first embodiment; and

FIG. 5 is a view similar to FIG. 4, but illustrating the elements in theseated or valve closed position.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. I schematically illustrates anairless spray system incorporating a pump in accordance with thisinvention. In this system, the coating material such as the zinc-richcoating material described above is located in a supply tank 10. A pump11 draws the material out of the tank through an intake line 12 anddischarges the coating material under pressure through a discharge line13 to an airless spray gun 14. The pump 11 includes a cylinder assembly16 an a piston assembly 17 reciprocable therein. The piston assembly 17is powered by a pneumatic piston and cylinder actuator 18. Thereciprocating operation of the actuator 18 is controlled by a valvemechanism 19 which connects the actuator 18 to an air pressure line 21through a shutoff valve 22. The United States Letters Patents referredto above disclose the structural details of a suitable pneumaticactuator and valve mechanism. The pump 11 is double-acting and suppliesmaterial at substantially the same pressure on each stroke of the pump.

The structural arrangement of the pump is best illustrated in FIG. 2.The cylinder assembly 6 includes a cylinder tube 26 threaded at itslower end into a valve body 27. Seals 28 and 29 prevent leakagetherebetween. The lower end of the valve body 27 is provided with athreaded inlet port 31 for connection to the intake line 12. The upperend of the tube 26 is threaded into a pump block 32 which is providedwith a threaded port 33 for connection to a fitting 34 on the end of thedischarge line 13. Here again, a seal 36 prevents leakage between thetube 26 and the pump block 32. The piston assembly 17 includes a pistonrod 37 which extends through the pump block 32 into the cylinder tube26. Mounted on the lower end of the piston rod 37 is a piston headassembly 38 which includes a chevron type packing 39 carried by a pistonhead member 41. A spring 42 extends between the packing assembly 39 anda stop ring 43 to compress the packing.

A second chevron type packing 44 is carried by the pump block 32 and iscompressed by a spring 46 which extends between it and the upper end ofthe cylinder tube 26. A lubrication cup 47 is formed in the pump block32 around the piston rod 37. The cylinder assembly I6 is divided by thepiston assembly 38 into a lower or main pump chamber 48 and an upper orsecondary pump chamber 49. Communication between the two chambers 48 and49 is controlled by a piston supported check valve assembly 51. A footvalve or inlet check valve assembly 52 is mounted in the valve body 27and permits flow only in a direction from the inlet line 12 toward themain pump chamber 48.

The check valve assembly 52 includes a valve seat member 53 formed witha spherical valve seat 54. The valve seat member 53 is positioned in thevalve body 27 against a shoulder 56. A ball valve 57 is movable into andout of engagement with the spherical valve seat 54 and is illustrated inFIGS. 2 and 3 in the closed position. A ball retainer 58 is mounted inthe valve body to retain the ball in position.

When the pressure in the main valve chamber 48 is lower than thepressure in the inlet port 31, which occurs on the upstroke of thepiston assembly 17, the ball valve 57 lifts away from the seat allowingflow into the main pump chamber. Conversely, on the downstroke of thepiston assembly, when the pressure in the main pump chamber exceeds thepressure in the inlet port 31, the ball valve 57 seats and prevents flowout of the main chamber toward the inlet port.

The piston check valve 51 includes a similar structure. Here again, avalve seat member 59 is formed with a spherical valve seat 61 and isseated against a shoulder 60 in the piston head member 41. A ball valve62 is sized to mate with the valve seat 61 and is movable from the openposition illustrated in FIG. 2 to a closed position in which it preventsflow from the secondary pump chamber 40 toward the main pump chamber 48.In this instance, a ball retaining pin 63 is provided to limit themovement of the ball 62 in a direction away from its associated valveseat 61. The ball 62 moves away from the seat 61, as illustrated, on thedownstroke of the piston and engages the seat on the upstroke of thepiston.

In the first embodiment of this invention, both of the ball valves 57and 62 have a structure as best illustrated in FIG. 3, and it should beunderstood that the following description of the ball 57 applies equallyto the ball 62. The ball 57 is provided with a spherical rigid core 66preferably formed of brass or the like which is encased within a jacket67 of elastomeric material. The outer surface 68 of the elastomericmaterial 67 is sized to mate with the associated valve seat 54 andprovide sealing engagement therewith as illustrated in FIG. 3. Oneelastomeric material which has been found to be particularly suitable ispolyurethane having a durometer sufficiently high so that it canwithstand the seating forces without sufficient deformation to causedamage but providing sufficient flexibility or elasticity to insureproper seating and sealing. Such polyurethane material provides goodwear characteristics since it is relatively tough and provides a surfacewith which the coating material such as zinc-rich coating materials donot form a weld type bond. In the illustrated embodiment, the sphericalvalve seat 54 is formed so that it provides an area engaged by the ball57 which is about 35 percent to 40 percent of the total area of the ball57. The piston check valve 51 in the illustrated embodiment is providedwith a spherical valve seat 61 having an area engaged by the ball 62which is about percent of the total area of the ball 62. The brass coreserves two functions. It provides rigidty and it adds weight to reducethe tendency of the ball to float in the coating material. In someinstances the ball may be formed of a homogeneous mixture of flexiblematerial such as polyurethane mixed with particles of heavy materialsuch as lead to increase weight. Such ball does not tend to form weldbonds because of the lower pressures encountered and because thepolyurethane again provides a surface to which the material does nottend to bond. Preferably, the valve seat 54 is provided with acurvedrelief section as illustrated at 69 so that the elastomeric material isnot cut during valve operation. In the first embodiment,-the valve seatmember 53 is formed of carbon steel or stainless steel since suchmaterial provides very good wear characteristics, however, othersuitable materials may be utilized.

Because the seat 54 is formed with a spherical shape which mates withthe exterior surface 68 of the ball 57, a substantial area of contact isprovided between the ball and the seat to resist the axial force appliedto the ball by the material within the associated chamber. Consequently,excessive pressures are not encountered between the mating surface andthe pressure of engagement is below the pressure required to cause aweld type deposit of the material on the valve seat 54. Consequently,deposits do not build up on the valve seat and the valve continues tofunction even when the pump is used to pump zinc-rich material or otherpowdered metal coating having a metal content up to 95 percent byweight. Such a valve also insures seating even if a slight roughnessdevelops along the valve seat because of the ability of the jacketmaterial 67 to deform and provide proper sealing.

In practice, a pump provided with such valves was found to have areliable service life, when pumping a zinc-rich coating, which wassubstantially as long as the service life experienced with conventionalvalves when pumping common paint coatings. The zinc-rich material withwhich such service life was established is marketed under the trade nameRust-Ban 193" by The Enjay Chemical Company. This material is a modifiedsodium lithium silicate stabilized with surfactants plus zinc powder andwater.

FIGS. 4 and 5 illustrate a second embodiment. Each of the check valvesis provided with a seat member 71 formed of tungsten carbide or the likeand a'ball valve member 72. The seat member 71 of this embodiment isagain formed with a spherical valve seat 73 provided with a curvedentrance 74. However, in this embodiment, an elastomeric O-ring seal 76is mounted within a groove 77 formed in the valve seat 73. The groove 77is located so that its upper wall extends in over the O- ring seal 76 toretain it in position even when the valve is in the open position ofFIG. 4. Here again, the ball valve 72 is formed with a rigid core 78 ofsteel or the like and an elastomeric jacket 79 preferably formed ofpolyurethane or the like. When the ball valve 72 is seated asillustrated in FIG. 5, the materials of both the O-ring and the jacket79 are deformed from their unstressed condition so that the jacket seatsagainst the valve seat 73 to limit the force of engagement between thetwo elastomeric materials and to limit the pressure of engagementtherebetween. In some instances, a valve seat assembly having an O-ringseal as illustrated in FIGS. 4 and 5 may be used with a unitary rigidball valve element which is not provided with an elastomeric jacket. Insuch a valve, the structure is arranged so that the pressure ofengagement between the O-ring and the ball valve is sufficiently low toprevent the weld type build-up of the coating material on the ball.

Since pumps incorporating this invention employ valves which includematerials with which zinc-rich coatings do not tend to form weld typebonds and since the structure is arranged to prevent the occurrence ofexcessive localized pressure, such pumps may be used for pumping suchzinc-rich materials without difficulty.

Although preferred embodiments of this invention are illustrated, itshould be understood that various modifications and rearrangements ofparts may be resorted to without departing from the scope of theinvention disclosed and claimed herein.

What is claimed is:

l. A pumping system comprising a source containing a zinc-rich coatingmaterial having a solid content of at least about 45 percent by volumeor the like, a pump having an inlet connected to said source operable topump said coating material from said source to said outlet at asubstantially increased pressure, said pump including a pair ofrelatively movable members cooperating to define a variable volume pumpchamber the volume of which is changed by relative movement of saidmembers, inlet and outlet check valves for controlling the flow of saidcoating material to and from said chamber, at least one of said valvesincluding a spherically curved seat element and a ball valve elementformed with mating surfaces of substantial area which are engagable toprevent backflow through said one valve, the area of the mating surfaceon said seat element being at least about 15 percent of the total areaof said ball element, at least one of said mating surfaces beingprovided by elastomeric material operating to distribute the force ofengagement between said elements evenly over said mating surfaces.

2. A pumping system as set forth in claim 1 wherein said zinc-richcoating material has a water base, said one valve is said inlet checkvalve, and said mating surface of said valve seat has an area from about15 percent to about 35 percent of the total area of said ball valveelement.

3. A pumping system as set forth in claim 2 wherein said elastomericmaterial is provided by said ball valve element and said seat element isprovided with a curved relief at least along the inlet side of saidspherical seat.

4. A pumping system as set forth in claim 3 wherein said ball valveelement is provided with a rigid core and a layer of elastomericmaterial enclosing said core.

5. A method of pumping water based zinc-rich materials or the likecomprising connecting a source of said zinc-rich material having a solidcontent of at least about 45 percent by volume to a pump having at leastone ball check valve which includes a seat and a ball, providing saidseat and ball with mating surfaces of substantial area which areengagable to prevent backflow, providing said mating surface of saidseat with an area at least about 15 percent of the total area of saidball, and forming at least one mating surface from an elastomericmaterial operating to evenly distribute the force of engagement betweensaid elements over said engaging and mating surfaces.

6. A method as set forth in claim 5 wherein said one ball check valve isthe inlet valve, the area of said mating surface of said seat is fromabout percent to about 35 percent of the total area of the ball.

7. A method as set forth in claim 6 including forming a curved relief onthe seat of the ball check valve at least along the inlet side of theseat therein.

8. In a pumping system including a source of zincrich coating materialhaving a solid content of at least about 45% by volume or the lilge. apump haying an outlet and an in le t connected to said source operableto pump said coating material from said source to said outlet at asubstantially increased pressure, said pump including a pair ofrelatively movable members cooperating to define a variable volume pumpchamber the volume of which is changed by relative movement of saidmembers, inlet and outlet check valves for controlling the flow of saidcoating material to and from said chamber, the improvement comprising atleast one of said valves including a spherically curved metal valve seatand a ball check valve comprising a substantially rigid metal coreencased within a layer of elastomeric material, said valve seat and saidball check valve having mating surfaces of substantial area withsubstantially the same radius of curvature, said mating surface of saidvalve seat having an area at least about 15% of the total area of saidball, said valve seat being provided with a curved relief adjacent tothe inlet side of said spherically curved seat, said surfaces beingengagable to prevent backflow through said one valve.

9. The improvement set forth in claim 8 wherein said layer ofelastomeric material is polyurethane.

10. The improvement set forth in claim 9 wherein said one valve is theinlet valve, and said mating surface of said valve seat has an area fromabout 15 percent to about 35 percent of the total area of said ballcheck valve.

11. In an airless spray pump for liquid coating material including apair of relatively movable members cooperating to define a variablevolume pump chamber the volume of which is changed by relative movementof said members, an inlet and an outlet to said chamber, inlet andoutlet check valves for controlling flow to and from said chamber, theimprovement comprising at least one of said valves including aspherically curved metal valve seat and a ball check valve comprising asubstantially rigid metal core encased within a layer of elastomericmaterial, said valve seat and said ball check valve having matingsurfaces of substantial area with substantially the same radius ofcurvature, said mating surface of said valve seat having an area atleast about 15 percent of the total area of said ball check valve, saidsurfaces being engagable to prevent backflow through said one valve.

12. The improvement set forth in claim 11 wherein said layer ofelastomeric material is polyurethane.

13. The improvement set forth in claim ll wherein said one valve is saidinlet valve.

14. The improvement set forth in claim 13 wherein said mating surface ofsaid valve seat has an area from about 15 percent to about 35 percent ofthe total area of said ball check valve.

1. A pumping system comprising a source containing a zinc-rich coatingmaterial having a solid content of at least about 45 percent by volumeor the like, a pump having an inlet connected to said source operable topump said coating material from said source to said outlet at asubstantially increased pressure, said pump including a pair ofrelatively movable members cooperating to define a variable volume pumpchamber the volume of which is changed by relative movement of saidmembers, inlet and outlet check valves for controlling the flow of saidcoating material to and from said chamber, at least one of said valvesincluding a spherically curved seat element and a ball valve elementformed with mating surfaces of substantial area which are engagable toprevent backflow through said one valve, the area of the mating surfaceon said seat element being at least about 15 percent of the total areaof said ball element, at least one of said mating surfaces beingprovided by elastomeric material operating to distribute the force ofengagement between said elements evenly over said mating surfaces.
 2. Apumping system as set forth in claim 1 wherein said zinc-rich coatingmaterial has a water base, said one valve is said inlet check valve, andsaid mating surface of said valve seat has an area from about 15 percentto about 35 percent of the total area of said ball valve element.
 3. Apumping system as set forth in claim 2 wherein said elastomeric materialis provided by said ball valve element and said seat element is providedwith a curved relief at least along the inlet side of said sphericalseat.
 4. A pumping system as set forth in claim 3 wherein said ballvalve element is provided with a rigid core and a layer of elastomericmaterial enclosing said core.
 5. A method of pumping water basedzinc-rich materials or the like comprising connecting a source of saidzinc-rich material having a solid content of at least about 45 percentby volume to a pump having at least one ball check valve which includesa seat and a ball, providing said seat and ball with mating surfaces ofsubstantial area which are engagable to prevent backflow, providing saidmating surface of said seat with an area at least about 15 percent ofthe total area of said ball, and forming at least one mating surfacefrom an elastomeric material operating to evenly distribute the force ofengagement between said elements over said engaging and mating surfaces.6. A method as set forth in claim 5 wherein said one ball check valve isthe inlet valve, the area of said mating surface of said seat is fromabout 15 percent to about 35 percent of the total area of the ball.
 7. Amethod as set forth in claim 6 including forming a curved relief on theseat of the ball check valve at least along the inlet side of the seattherein.
 8. In a pumping system including a source of zinc-rich coatingmaterial having a solid content of at least about 45% by volume or thelike, a pump having an outlet and an inlet connected to said sourceoperable to pump said coating material from said source to said outletat a substantially increased pressure, said pump including a pair ofrelatively movable members cooperating to define a variable volume pumpchamber the volume of which is changed by relative movement of saidmembers, inlet and outlet check valves for controlling the flow of saidcoating material to and from said chamber, the improvement comprising atleast one of said valves including a spherically curved metal valve seatand a ball check valve comprising a substantially rigid metal coreencased within a layer of elastomeric material, said valve seat and saidball check valve having mating surfaces of substantial area withsubstantially the same radius of curvature, said mating surface of saidvalve seat having an area at least about 15% of the total area of saidball, said valve seat being provided with a curved relief adjacent tothe inlet side of said spherically curved seat, said surfaces beingengagable to prevent backflow through said one valve.
 9. The improvementset forth in claim 8 wherein said layer of elastomeric material ispolyurethane.
 10. The improvement set forth in claim 9 wherein said onevalve is the inlet valve, and said mating surface of said valve seat hasan area from about 15 percent to about 35 percent of the total area ofsaid ball check valve.
 11. In an airless spray pump for liquid coatingmaterial including a pair of relatively movable members cooperating todefine a variable volume pump chamber the volume of which is changed byrelative movement of said members, an inlet and an outlet to saidchamber, inlet and outlet check valves for controlling flow to and fromsaid chamber, the improvement comprising at least one of said valvesincluding a spherically curved metal valve seat and a ball check valvecomprising a substantially rigid metal core encased within a layer ofelastomeric material, said valve seat and said ball check valve havingmating surfaces of substantial area with substantially the same radiusof curvature, said mating surface of said valve seat having an area atleast about 15 percent of the total area of said ball check valve, saidsurfaces being engagable to prevent backflow through said one valve. 12.The improvement set forth in claim 11 wherein said layer of elastomericmaterial is polyurethane.
 13. The improvement set forth in claim 11wherein said one valve is said inlet valve.
 14. The improvement setforth in claim 13 wherein said mating surface of said valve seat has anarea from about 15 percent to about 35 percent of the total area of saidball check valve.